1. Field of the Invention
The present invention generally relates to magnetic resonance, high resolution spectroscopy machines and, in particular, to such machines used for testing large numbers of samples.
2. Statement of the Prior Art
Magnetic resonance or nuclear magnetic resonance has been used for spectral analysis of liquids and solids for many years. Recently renewed interest in an easy method for performing spectral analysis on a large number of samples has been sparked by certain lipoprotein lipids in blood plasma being tied to the presence of cancer in the body. It is hoped that such lipid measurements could be used as a screening test for early detection of cancer and as a means for monitoring the progress of cancer therapy and for optimization thereof. This would minimize patients' exposure to treatment side effects and improve the accuracy of cancer detection.
For these purposes, it is necessary to provide a spectroscopy apparatus which economically maintains several critical measurement parameters and is easy to operate and capable of handling large numbers of test samples. Thus far, the only instruments available have been research labaratory instruments which are not well suited to clinical application. Generally, the process is performed in a high intensity, static magnetic field. The field is made as uniform as possible by a process known as shimming which applies additional magnetic fields to compensate for incongruities in the main field. Once the sample is introduced into the field, it is spun at a constant rate and the field is again shimmed. Spinning the sample helps to further improve spectral resolution by averaging field inhomogeneities that cannot be removed by shimming and for inconsistencies in the sample.
Measurements are performed by administering pulses of radio frequency (r.f.) energy transmitted by a radio frequency coil which is located within the magnetic field and around the sample. Immediately after a pulse, the coil is monitored for radio frequency energy which is retransmitted from nuclei returning to the orientation caused by the magnetic field. The amount of r.f. energy received at various frequencies indicates the sample constituents. Different constituents absorb the transmitted r.f. energy at different frequencies.
Various approaches have been used for performing these operations within the high intensity field. One common approach uses a high field superconducting magnet system having a vertical bore into which the test tube samples are lowered. A rotor for an air motor is affixed to the sample test tube. The stator for the motor is located within the magnetic field, and the test tube and rotor are lowered into the magnetic field for each test. The portion of the sample to be tested extends past the stator into an area where the radio frequency coil is located. This coil is mounted as part of a formed glass cylinder which surrounds the volume which is actually excited and measured for magnetic resonance. Air is supplied to the stator to create an air bearing and to cause the rotor to spin. Once the rotor and test tube are up to speed, the magnetic resonance testing is performed and the rotor and test tube are then removed. Movement of the rotor and test tube into and out of the magnetic field and stator is commonly performed by compressed air working against the force of gravity. The sample is typically delivered to and from the bore by some mechanism such as a conveyor belt, rotating tray or a robot arm. This approach with several variations are disclosed in U.S. Pat. Nos. 2,960,649; 3,100,866; 3,287,630; 3,462,677; 3,512,078; 3,796,946; 3,911,533; 4,088,944; and 4,240,033.
Unfortunately, this approach has several limitations and drawbacks. Most expensively, a seperate rotor is required for each test tube. While the rotors maybe reused, the test tubes must either be cleaned or replaced in each rotor after a test. Cleaning is difficult because the rotor cannot suffer any abuse. It is typically precision made and balanced to minimize the introduction of spin vibrations into the sample. These vibrations affect the accuracy of the test. The rotors cannot be dented or stained with anything as this will cause an imbalance. Meanwhile, the rotors are expensive and frequent replacement even raises further the already high cost of using large numbers of rotors.
There are also limitations on the spin speed of the sample using this method. As compressed air and gravity are used to move the test tube and rotor into and out of the stator, using too much compressed air to spin the sample at higher speeds causes ejection of the rotor and sample from the apparatus and usually damage. Of course, breakage of the test tube either within or over the magnetic field can cause very expensive damage as the radio frequency coil may easily be damaged and any contamination within the apparatus must be thoroughly cleaned by means of disassembly.
A further disadvantage is the requirement for large amounts of very clean air and temperature contamination of the sample thereby. The air used in an air motor must be very clean because the size of the air bearing is small enough so that any oil, moisture or particles can affect or prevent operation. Half micron filtering is commonly used for this air. Because this air is also used for levitating the test tube and rotor, very large volumes are required. Lastly, temperature control is very important in hematology, and control of the motor air temperature is difficult at best given the compression and expansion to which it is subjected. This air is often in contact with the test tube and thus causes temperature instability. Means have been devised for applying temperature controlled air directly to the test tube in the area of the sample. Although helping to solve one problem, this contributes to air pressure build up beneath the test tube and rotor.
A still further disadvantage of previously used methods is the expense and bulk of the required sample handling apparatus. Often, this apparatus becomes large than the superconducting magnet. Apparatus of this nature also has a significant effect on the magnetic field of the magnet, which effect must be compensated for in the shimming process. Lastly, certain types of apparatus tend to malfunction when operating in the high magnetic field.
In view of these difficulties with the prior art, the desirable aspects of a clinical machine are typically as follows: ease of handling of the test tubes; safety factors in tube handling to prevent tube breakage within the bore and thus expensive bore replacement; ease of sample temperature stabilization including minimizing the effects of spin air on the temperature of the sample; simplicity in the test tube handler to reduce the possibillities of failure; and rotor and test tube cost. Other desireable aspects include ease of aligning the test tube about the center of rotation including the repeatability of this alignment, ease of stabilizing both the rotation of the tube about the center of rotation and the spin speed, and minimized effects of the tube handling apparatus on the magnetic fields.